CVE-2026-59929: Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution
Vulnerability summary
CVE-2026-59929 is a medium (CVSS 6.1) vulnerability in lepture mistune. EPSS estimates a 0.34% chance of exploitation in the next 30 days, higher than 27.7% of scored vulnerabilities. 1 public exploit is recorded.
Not severe (CVSS 6.1, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 2 · Related 2Timeline
- 08-07-2026PublishedVulnerability first disclosed.
- 09-07-2026Last modifiedVulnerability information updated.
Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res: to reach rendered href and src attributes and potentially execute script in affected user agents. This issue is fixed in version 3.3.0.
CVSS metrics
5 scores · 5 sources · 1 version- OSV · PypiEcosystem advisory · calculated6.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- OSV · UbuntuEcosystem advisory · calculated6.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- OSV · DebianEcosystem advisory · calculated6.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- NVDNIST6.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS trend
Probability
0.34%
Chance of exploitation in the next 30 days
Percentile
28%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.34% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
1 foundMistune
Maturity: poc
Weaknesses
CWE · root cause- CWE-79Improper Neutralization of Input During Web Page GenerationThe product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
- CWE-184Incomplete List of Disallowed InputsThe product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.
Affected systems
Known conditions: network-reachable, no authentication, user interaction (CVSS vector). Other conditions: not stated in public data.
Debian1 product
- mistuneAll versions (No fix recorded)
Lepture1 product
- mistune< 3.3.0
Mistune_project1 product
- mistune< 3.3.0
PyPI1 product
- mistune< 3.3.0
Ubuntu1 product
- mistuneAll versions (No fix recorded)
5 vendors · 5 products
References
9 links- github.com/lepture/mistune/security/advisories/GHSA-qfrw-5rxm-mhh2X Refsource CONFIRMWEBEVIDENCEREPORTExploitThird Party Advisory
- github.com/lepture/mistune/commit/c7101fcbb6e8790e8e39157c5ca2238fc6dd6cbcX Refsource MISCWEBFIXPatch
- github.com/lepture/mistunePACKAGE
